In an electrical power conversion device for use in high-voltage applications, it is made possible to achieve a multilevel converter to go into practical use. A multilevel converter is disclosed with its circuit configuration in which a plurality of converter cells is connected in series with one another between AC terminals U, V and W, and DC terminals P and N; and, in accordance with turn-on/turn-off control of semiconductor switching elements intrinsically exist in the converter cells, AC voltages are generated at the AC terminals U, V and W, and DC voltages, at the DC terminals P and N (for example, refer to Non-Patent Documents 1, 2). In Non-Patent Document 1, half-bridge converter cells referred to as chopper-cells are used. In addition to half-bridge converter cells, in Non-Patent Document 2, converter cells configured in so-called full-bridges using two legs (converter-legs) are also utilized.
Meanwhile, there exists a power conversion device in which, when abnormality occurs in its converter cell (sub-module), output terminals of the converter cell (sub-module) where the abnormality occurs are bypassed by a bypass element (short-circuit device), and continuous operations are made possible (for example, refer to Patent Documents 1 and 2).